package com.westos.userauth.util;

/**
 * @Author: Youzg
 * @CreateTime: 2020-10-31 16:56
 * @Description: 带你深究Java的本质！
 */
public class SnowflakeIdUtils {
    private final static int PARTY_TYPE = 0;
    private final static int USER_TYPE = 1;

    private final long twepoch = 1420041600000L;
 
    private final long workerIdBits = 5L;
 
    private final long datacenterIdBits = 5L;
 
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
 
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
 
    private final long sequenceBits = 12L;
 
    private final long workerIdShift = sequenceBits;
 
    private final long datacenterIdShift = sequenceBits + workerIdBits;
 
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
 
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);
 
    private long workerId;
 
    private long datacenterId;
 
    private long sequence = 0L;
 
    private long lastTimestamp = -1L;
 
    /**
     * 构造函数
     * @param workerId 工作ID (0~31)
     * @param datacenterId 数据中心ID (0~31)
     */
    public SnowflakeIdUtils(long workerId, long datacenterId) {
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }

    /**
     * 构造函数
     * @param typeId 类别ID (0~31)
     */
    public SnowflakeIdUtils(Integer typeId) {
        this(typeId, typeId);
    }

    /**
     * 获得下一个ID (该方法是线程安全的)
     * @return SnowflakeId
     */
    public synchronized long nextId() {
        long timestamp = timeGen();
 
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(
                    String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }
 
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        }
        else {
            sequence = 0L;
        }
 
        lastTimestamp = timestamp;
 
        return ((timestamp - twepoch) << timestampLeftShift) //
                | (datacenterId << datacenterIdShift) //
                | (workerId << workerIdShift) //
                | sequence;
    }
 
    /**
     * 阻塞到下一个毫秒，直到获得新的时间戳
     * @param lastTimestamp 上次生成ID的时间截
     * @return 当前时间戳
     */
    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }
 
    /**
     * 返回以毫秒为单位的当前时间
     * @return 当前时间(毫秒)
     */
    protected long timeGen() {
        return System.currentTimeMillis();
    }

    ///** 测试 */
    //public static void main(String[] args) {
    //    SnowflakeIdUtils idWorker = new SnowflakeIdUtils(PARTY_TYPE, PARTY_TYPE);
    //    System.out.println(idWorker.nextId());
    //    System.out.println(idWorker.nextId());
    //}
}